A Fragmentary Dinosaur Femur and the Presence of Neotheropoda in the Upper Triassic of Brazil

A FRAGMENTARY DINOSAUR FEMUR AND THE PRESENCE OF NEOTHEROPODA IN THE UPPER TRIASSIC OF BRAZIL

FELIPE L. PINHEIRO Laboratório de Paleobiologia, Universidade Federal do Pampa, Campus São Gabriel, R. Aluízio Barros Macedo, BR 290, km 423, CEP 97300-000, São Gabriel, RS, Brazil. [email protected]

ABSTRACT – Although already widespread in Laurasia, the Gondwanan Norian record of Neotheropoda (Dinosauria) is scarce, with a single taxon reported for the Los Colorados Formation of Argentina. Here the distal end of a dinosaur left femur from the Riograndia Assemblage Zone of Brazil (Norian, Candelária Sequence, Paraná Basin) is described and compared. Although fragmentary, the specimen has a morphology compatible with its attribution to Neotheropoda, being this the first record of the clade from the Brazilian Triassic. The new specimen supports a cosmopolitan distribution of Neotheropoda during the Late Triassic and highlights the potential for the discovery of additional dinosaur clades in Norian rocks of southern Brazil.

Key words: Dinosauria, Gondwana, Norian, Theropoda.

RESUMO – Apesar de já bem distribuído no Laurásia, o registro gondwânico dos Neotheropoda (Dinosauria) é escasso no Noriano, com apenas um táxon reportado para a Formação Los Colorados da Argentina. Aqui é descrito um fragmento distal de um fêmur esquerdo de dinossauro, proveniente da Zona de Assembleia de Riograndia (Noriano, Sequência Candelária, Bacia do Paraná, Brasil). Embora fragmentário, o espécime apresenta morfologia compatível com sua atribuição a Neotheropoda, sendo este o primeiro registro deste táxon para o Triássico brasileiro. O novo espécime suporta uma distribuição cosmopolita dos Neotheropoda durante o Neotriássico, além de evidenciar o potencial de rochas do Noriano brasileiro para a descoberta de uma diversidade ainda oculta de dinossauros.

Palavras-chave: Dinosauria, Gondwana, Noriano, Theropoda.

INTRODUCTION in that continent (Arcucci & Coria, 2003; Ezcurra & Novas, 2007). The Upper Triassic sedimentary record of Western Here, the distal end of a dinosaur left femur from a Pangaea, especially as represented by the Chañares, classic locality of the Riograndia AZ is described. The Ischigualasto and Los Colorados formations of Argentina specimen is unlike the other taxa so far recorded for the and the Candelária Sequence of Brazil (sensu Horn et al., Candelária Sequence and has a morphology compatible with 2014), provides rich and unique insights into the origins and Neotheropoda, indicating the presence of this clade in the early diversification of dinosaurs (e.g. Arcucci et al., 2004; Upper Triassic of Brazil. Langer et al., 2010b; Marsicano et al., 2016). Compared Institutional abbreviations. MMACR, Museu Municipal with the well-sampled coeval deposits of Argentina, Aristides Carlos Rodrigues, Candelária, RS, Brazil; dinosaur diversity in Brazilian Late Triassic is still low, NMMNH, New Mexico Museum of Natural History with only a few taxa known from the Hyperodapedon & Science, Albuquerque, New Mexico, USA; SMNS, Assemblage Zone (AZ) and the younger Riograndia AZ Staatliches Museum für Naturkunde, Stuttgart, Germany. (Norian) of the Candelária Sequence (Paraná Basin, e.g. Langer et al., 2010b) (Figure 1). Although neotheropod SYSTEMATIC PALAEONTOLOGY dinosaurs were relatively widespread during the Norian, this clade has not been previously reported from the Riograndia Clade DINOSAURIA Owen, 1842 AZ of Brazil. As a matter of fact, even though neotheropod Suborder THEROPODA Marsh, 1881 remains have been recovered from a number of mainly Clade NEOTHEROPODA Bakker, 1986 Laurasian norian fossil sites, representatives of this clade (Figures 2A-J) were rare during the Late Triassic. Only one neotheropod taxon is known for South American Upper Triassic, despite Material. MMACR 039 T, distal portion of a left femur the fact that rocks of this series are well represented (Figures 2A-J).

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Locality, unit and age. The specimen comes from the The distal end is only slightly expanded lateromedially ‘Botucaraí Hill’, a well-known Riograndia AZ site in relation to the shaft, a condition not observed in most (Norian, Candelária Sequence, Paraná Basin) located in a Triassic dinosaurs, such as herrerasaurids (e.g. Novas, 1993), road cut 6 km west of Candelária city, Rio Grande do Sul, sauropodomorphs (e.g. Langer, 2003; Müller et al., 2015), Brazil (29°40’53”S; 52°50’28”W). The outcrop exposes Guaibasaurus (Bonaparte et al., 1999; Langer et al., 2010a) sandstones intercalated with mudstone lenses. Remains of and ornithischians (e.g. Butler, 2010). sauropodomorphs from the ‘Botucaraí Hill’ site were reported The distal anterior surface bears a faint extensor groove by Bittencourt et al. (2013). The Norian age of ‘Botucaraí that is connected distally with a very discrete sulcus Hill’ site is based on the presence of the dicynodont genus intercondylaris (Figures 2A,B). An extensor groove is Jachaleria, also known from the lower levels of the Los regarded as a derived character, present in some abelisauroids Colorados Formation (Soares et al., 2011). and tetanurans (Ezcurra & Novas, 2007), but absent in Comparative description. MMACR 039 T (Figures 2A-J) herrerasaurids, basal sauropodomorphs such as Saturnalia, is well preserved, lacking strong diagenetic alterations. The basal ornithischians, such as Lesothosaurus and Eocursor, proximal end and most of the shaft are missing, and there is as well as some early theropods, such as Liliensternus, a superficial breakage that partially excavates the anterior Coelophysis, Tawa and Zupaysaurus (e.g. Langer, 2003; surface of the bone. The preserved fragment is 37 mm long Ezcurra & Novas, 2007; Butler, 2010). The distal femur of and 21 mm in lateromedial width, and measures 15 mm herrerasaurids, Saturnalia, Eocursor and Tawa has a distinctly between its anterior margin and the posterior most extension convex anterior surface. Guaibasaurus, Pampadromaeus, of the medial (tibial) condyle. Eoraptor and Coelophysis (NMMNH 42351), although

Figure 1. Southern Brazil Triassic chronostratigraphy, depicting vertebrate biozones and recovered dinosaur taxa. Modified from Zerfass et al. (2003) and Horn et al. (2014). Saturnalia, Pampadromaeus and Staurikosaurus silhouettes modified from Pretto et al. (2015). PINHEIRO ET AL. – NEOTHEROPODA IN THE UPPER TRIASSIC OF BRAZIL 213 having a flat femoral anterior surface, lack an extensor groove surface (Figures 2I,J). This contrasts with the obtuse-angled (Bonaparte et al., 1999; Ezcurra & Novas, 2007; Sereno et distal anteromedial corner developed in a number of basal al., 2013; Müller et al., 2015). dinosaurs. This character, however, is considerably variable A U-shaped popliteal fossa excavates the posterior among early dinosaurs, and may be influenced by size. surface of the specimen (Figures 2I,J). The depth of this An anteromedial corner forming an acute angle is more fossa resembles the condition observed in Saturnalia, widespread among neotheropods, being present, for example, Pampadromaeus, Eoraptor and neotheropods, and is in Dilophosaurus, Streptospondylus (Welles, 1984; Allain, deeper than in herrerasaurids (Novas, 1993; Langer, 2003; 2001) and Liliensternus (based on a replica of the syntype, Bittencourt & Kellner, 2009; Alcober & Martínez, 2010; deposited at the SMNS). On its posterior surface, the medial Sereno et al., 2013; Müller et al., 2015). condyle of MMACR 039 ends in a small prominence, flanked The medial condyle is anteroposteriorly oriented, forming ventromedially by a deep sulcus. This unusual structure is here an angle of a little less than 90° with the femoral anterior interpreted as an epicondyle (Figures 2C,D).

A B C D

eg ctf mc

E F G H I

mc dg J fc

ctf fc mc pf mc ctf K L M N fc fc fc fc pf mc mc mc pf mc pf ctf pf ctf ctf ctf

Figure 2. A-J, specimen MMACR 039 T, photographs and interpretative drawings in A-B, anterior; C-D, posterior; E-F, lateral; G-H, medial and I-J distal views. K-N, selected Triassic dinosaur femora in distal view. K, Herrerasaurus (redrawn from Novas, 1993, mirrored). L, Pampadromaeus (redrawn from Müller et al., 2015). M, Eocursor (redrawn from Butler, 2010, mirrored). N, Liliensternus. Abbreviations: ct, crista tibiofibularis; dg, distal groove; eg, extensor groove; ep, epicondyle; fc, fibular condyle; mc, medial condyle; pf, popliteal fossa. Scale bar: A-J = 20 mm; K-N = not to scale. 214 REVISTA BRASILEIRA DE PALEONTOLOGIA, 19(2), 2016

The crista tibiofibularis is deflected laterally, tapering lack of an elevation posterior to the distal groove (as is posterolaterally into a pointed tip (Figures 2I,J), being the condition in MMACR 039 T) is characteristic of basal separated from the rounded fibular condyle by a well- theropods, such as Liliensternus. Of particular relevance developed lateral groove, a distinctive feature of neotheropods. is the presence of an extensor groove on the anterior A laterally deflected crista tibiofibularis is widespread among surface of the femur, a character that, although better neotheropods (e.g. Welles, 1984; Allain, 2001), but is also developed in more derived tetanurans, is also present in present in Sauropodomorpha (e.g. Saturnalia, Plateosaurus) some abelisauroids (Ezcurra & Novas, 2007; Carrano et and silesaurids (e.g. Sacisaurus), although generally to a lesser al., 2012). The distribution of this character among basal degree than represented in MMACR 039 T (Langer, 2003, fig. neotheropods, however, needs further investigation. 4; Langer & Ferigolo, 2013, fig. 17). The crista tibiofibularis A yet undescribed silesaurid from the Carnian of Poland of Eoraptor, albeit laterally deflected, has a rounded outline shares with MMACR 039 T a laterally deflected, pointed (Sereno et al., 2013). tibiofibular crest, separated from the fibular condyle by a In distal view, MMACR 039 T displays a deep, mostly deep sulcus (G. Niedźwiedzki, personal communication). straight, distal groove (Figures 2I,J), anterior to which the The femur of the new silesaurid, however, lacks an extensor distal surface expands to form the distal corpus of the fibular groove and has a convex anterior margin that forms an obtuse condyle. A posterior expansion is absent (Figures 2E,F), angle with the medial condyle. contrasting with the condition of basal sauropodomorphs, Despite its fragmentary condition, the morphology of such as Saturnalia and Pampadromaeus, where the distal MMACR 039 T supports a neotheropod affinity for the surface is also elevated posteriorly, contributing to the crista specimen, at least until further evidence proves otherwise. The tibiofibularis (Langer, 2003; Mülleret al., 2015). presence of a tibiofibular crest that is sharply distinguished from the fibular condyle by a deep sulcus is regarded by DISCUSSION Ezcurra & Novas (2007) as a probable synapomorphy of the Coelophysoidea, perhaps indicating the attribution of MMACR 039 T can be distinguished from known MMACR 039 T to this clade. Eoraptor lunensis, however, also herrerasaurids (Figure 2K) by the presence of a deep popliteal presents a moderately deep groove between the tibiofibular fossa, an incipient extensor groove on its anterior surface crest and the fibular condyle (Sereno et al., 2013). It is and a laterally deflected, pointed, tibiofibular crest, separated remarkable that the ratio between the lateromedial width and from the fibular condyle by a sharp groove (Novas, 1993; the anteroposterior length of MMACR 039 T closely matches Alcober & Martínez, 2010; Bittencourt & Kellner, 2009). that in Coelophysis (NMMNH 42351). An extensor groove and a tibiofibular crest separated from The oldest neotheropods are known from fragmentary the fibular condyle by a deep sulcus are also absent in most bones from the upper Carnian Chinle Formation, Arizona, silesaurids (e.g. Sacisaurus, but see below), sauropodomorphs and Dockun Group, Texas, USA (Hunt et al., 1998; Nesbitt (Figure 2L) and early ornithischians (Figure 2M), from which et al., 2007; Nesbitt & Ezcurra, 2015, but see Ramezani MMACR 039 T can also be distinguished by the anterior et al., 2014). Throughout the Norian, the Neotheropoda margin of the distal femur forming an angle close to 90° became relatively widespread, with several described taxa with the medial one. Moreover, basal ornithischians, such as preserved mainly in Laurasian Upper Triassic deposits (see Eocursor, have a markedly convex anterior surface on their Langer et al., 2010b; Brusatte et al., 2010; Niedźwiedzki distal femur, formed mainly by an anterolateral projection et al., 2014 and references therein for a review). The of the fibular condyle e.g.( Butler, 2010, fig. 15). A similar Gondwanan Norian neotheropod record is still scarce. In condition is also present in silesaurids such as Sacisaurus the South American Triassic, this clade is represented only (Langer & Ferigolo, 2013). by the coelophysoid Zupaysaurus rougieri from the upper Several features are consistent with the attribution of levels of Los Colorados Formation (Arcucci & Coria, 2003; MMACR 039 T to Neotheropoda (Figure 2N). An acute Ezcurra & Novas, 2007) and fragmentary remains from the angle formed between the medial margin of the medial Quebrada del Barro Formation, northwestern Argentina condyle and the anterior surface of the distal femur, (Martínez et al., 2015). Remarkably, the fossil assemblage although also present in some herrerasaurids is common of ‘Botucaraí Hill’ probably correlates to the basal level of among neotheropods (see above). This is also true for Los Colorados Formation, what is suggested by the presence a laterally deflected, pointed tibiofibular crest, albeit of the dicynodont genus Jachaleria in both Argentinean this feature also seems to be widespread among basal and Brazilian deposits (Soares et al., 2011). Therefore, the sauropodomorphs (e.g. Langer, 2003) and silesaurids (e.g. attribution of MMACR 039 T to Neotheropoda makes it the Langer & Ferigolo, 2013). In addition, the presence of a oldest representative of this clade in South America. small epicondyle on the posterior surface of the medial The presence of a neotheropod in Norian strata of Brazil condyle was regarded by Ezcurra & Novas (2007) as a extends the Late Triassic distribution of this group in Western potential synapomorphy of Neotheropoda, even though Gondwana. Furthermore, the new specimen draws attention this feature is not thorough discussed by these authors to the still hidden dinosaur diversity in the Upper Triassic of and its distribution among basal theropods needs further Brazil, a shortcoming that will be addressed by more intensive clarification. Furthermore, Langer (2003) observed that the collection efforts. PINHEIRO ET AL. – NEOTHEROPODA IN THE UPPER TRIASSIC OF BRAZIL 215

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